U.S. patent application number 10/405913 was filed with the patent office on 2004-05-13 for image signal processing system and camera having the image signal processing system.
Invention is credited to Kohashi, Atsushi, Mori, Keiichi.
Application Number | 20040091145 10/405913 |
Document ID | / |
Family ID | 29243207 |
Filed Date | 2004-05-13 |
United States Patent
Application |
20040091145 |
Kind Code |
A1 |
Kohashi, Atsushi ; et
al. |
May 13, 2004 |
Image signal processing system and camera having the image signal
processing system
Abstract
Briefly, a camera according to the present invention includes a
first signal processing system having a first gamma conversion
processing unit for subjecting an output from an image pick-up
device to gamma conversion processing and a luminance signal
generating unit for generating a luminance-system signal based on
an output from the first gamma conversion processing unit, and a
second signal processing system having a color signal generating
unit for generating a color-system signal based on an output which
is the output from the image pick-up device and which is not
subjected to the gamma conversion processing.
Inventors: |
Kohashi, Atsushi; (Tokyo,
JP) ; Mori, Keiichi; (Tokyo, JP) |
Correspondence
Address: |
STRAUB & POKOTYLO
620 TINTON AVENUE
BLDG. B, 2ND FLOOR
TINTON FALLS
NJ
07724
US
|
Family ID: |
29243207 |
Appl. No.: |
10/405913 |
Filed: |
April 2, 2003 |
Current U.S.
Class: |
382/162 ;
348/222.1; 348/E9.042; 348/E9.054 |
Current CPC
Class: |
H04N 9/646 20130101;
H04N 9/69 20130101; G06T 5/009 20130101; G06T 2207/10016 20130101;
H04N 2101/00 20130101 |
Class at
Publication: |
382/162 ;
348/222.1 |
International
Class: |
G06K 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 11, 2002 |
JP |
2002-109660 |
Claims
What is claimed is:
1. A camera comprising: a first signal processing system comprising
first gamma conversion processing means for subjecting an output
from an image pick-up device to gamma conversion processing and
luminance signal generating means for generating a luminance-system
signal based on the output from the first gamma conversion
processing means; and a second signal processing system comprising
color signal generating means for generating a color-system signal
based on an output which is the output from the image pick-up
device and which is not subjected to the gamma conversion
processing.
2. The camera according to claim 1, wherein the second signal
processing system generates a color difference signal as the
color-system signal.
3. The camera according to claim 1, wherein the first signal
processing system comprises edge emphasis processing means and
coring processing means at a later stage than the first gamma
conversion processing means.
4. The camera according to claim 1, wherein the second signal
processing system comprises, by inserting in its signal
transmitting path, color correction processing means used for color
correction processing and second gamma conversion processing means
used for the gamma conversion processing performed at a later stage
than the color correction processing means.
5. The camera according to claim 1, wherein the second signal
processing system comprises band limiting means independently of
the first signal processing system.
6. The camera according to claim 1, wherein the first signal
processing system and the second signal processing system are
digital systems.
7. An image signal processing system comprising: an input terminal
portion which is arranged to receive an output signal from an image
pick-up device having a predetermined-type color filter on the side
of an image pick-up surface or to receive a color image pick-up
signal substantially equivalent to the output from the image
pick-up device; a first signal processing system comprising first
gamma conversion processing means used for subjecting to gamma
conversion processing the signal supplied from the input terminal
portion and luminance signal generating means for generating a
luminance-system signal based on an output from the first gamma
conversion processing means; and a second signal processing system
comprising color signal generating signal means for generating a
color-system signal based on an output which is the output from the
image pick-up device and which is not subjected to the gamma
conversion processing.
8. The image signal processing system according to claim 7, wherein
the first signal processing system comprises edge emphasis
processing means and coring processing means at later stages than
the first gamma conversion processing means.
9. The image signal processing system according to claim 7, wherein
the second signal processing system comprises, by inserting in its
signal transmitting path, color correction processing means for
color correction processing and second gamma conversion processing
means for the gamma conversion processing performed at a later
stage than the color correction processing means.
10. The image signal processing system according to claim 7,
wherein the second signal processing system comprises band limiting
means independently of the first signal processing system.
11. The image signal processing system according to claim 7,
wherein the first signal processing system and the second signal
processing system are digital systems.
Description
[0001] This application claims benefit of Japanese Application No.
2002-109660 filed in Japan on Apr. 11, 2002, the contents of which
are incorporated by this reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an image signal processing
system and a camera having the image signal processing system.
[0004] 2. Description of the Related Art
[0005] Conventionally, a so-called electronic still camera or a
digital camera (hereinafter, referred to as an electronic camera or
simply referred to as a camera) is generally and widely spread. In
the electronic camera, a subject image which is optically formed by
using a photographing optical system having a photographing lens
and the like is photoelectrically converted by image pick-up means
including an image pick-up device and the like such as a charge
coupled device (hereinafter, briefly referred to as a CCD). The
photoelectrically converted electrical signal (image signal
indicating an image) is subjected to compression processing such as
a predetermined-form image data (e.g., JPEG (Joint Photographic
Experts Group)) method and is electronically recorded.
[0006] In the conventional electronic camera using the CCD as the
image pick-up means, normally, an output signal, namely, an image
signal generated and outputted through photoelectric conversion
processing using the image pick-up device (CCD) mixedly includes
random noises such as shot noise.
[0007] Then, in the above-mentioned conventional electronic camera,
an operation for displaying a preferred image to display means
generally requires various signal processing for suppressing or
removing noise components and the like from an output signal (image
signal) from the image pick-up device (CCD). Usually, an operation
for accurately displaying the subject image to be displayed based
on the image signal further requires various signal processing of
the image signal, such as various correction processing.
[0008] Hence, the general and conventional electronic camera
comprises a system for generating an image signal or image data
which is most proper to a display operation of the image or a
recording operation of the electrical signal indicating the image
based on the output signal from the image pick-up device (CCD),
namely, an image signal processing system.
[0009] For example, Japanese Unexamined Patent Application
Publication No. 9-130816, Japanese Unexamined Patent Application
Publication No. 11-112837, etc. propose the above-mentioned
conventional image signal processing systems.
[0010] In the image signal processing system disclosed in Japanese
Unexamined Patent Application Publication No. 9-130816, the image
signal is subjected to coring processing and gamma correction
processing. Further, the image signal is subjected to edge emphasis
processing (contour correction processing), luminance signal
generation processing, and chroma signal generation processing
based on the output signal generated by the gamma correction
processing.
SUMMARY OF THE INVENTION
[0011] Accordingly, it is an object of the present invention to
provide an image signal processing system for generating preferable
image data by devising various signal processing performed based on
an image signal captured by an image pick-up device, and a camera
using the image signal processing system.
[0012] Briefly, a camera according to the present invention
includes a first signal processing system having a first gamma
conversion processing unit for subjecting to gamma conversion
processing an output from an image pick-up device and a luminance
signal generating unit for generating a luminance-system signal
based on an output from the first gamma conversion processing unit,
and a second signal processing system having a color signal
generating unit for generating a color-system signal based on an
output which is the output from the image pick-up device and which
is not subjected to the gamma conversion processing.
[0013] This feature and advantages of the present invention will
become further apparent from the following detailed
explanation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a block diagram schematically showing an image
signal processing system in a camera according to an embodiment of
the present invention;
[0015] FIG. 2 is a diagram showing the alignment of color filter
arrays arranged in front of a CCD of the camera shown in FIG.
1;
[0016] FIG. 3 is a diagram showing the concept of gamma correction
processing of a Y.gamma. unit in the image signal processing system
shown in FIG. 1;
[0017] FIG. 4 is a diagram showing coordinates of a luminance
signal corresponding to a CCD output signal shown in FIG. 2;
[0018] FIG. 5 is a diagram showing an HPF coefficient of a spatial
filter (HPF) for extracting an edge in the image signal processing
system shown in FIG. 1;
[0019] FIG. 6 is a diagram showing the concept of coring processing
in the image signal processing system shown in FIG. 1;
[0020] FIG. 7 is a diagram showing the concept of synchronization
processing in the image signal processing system shown in FIG.
1;
[0021] FIG. 8 is a diagram showing an LPF coefficient of a spatial
filter (LPF) for limiting a band in the image signal processing
system shown in FIG. 1;
[0022] FIG. 9 is a diagram showing a processing result of the gamma
correction processing in the image signal processing system shown
in FIG. 1;
[0023] FIG. 10 is a diagram showing a processing result of edge
emphasis processing in the image signal processing system shown in
FIG. 1;
[0024] FIG. 11 is a diagram showing a setting value of a coring
threshold level in the image signal processing system shown in FIG.
1;
[0025] FIG. 12 is a diagram showing a processing result of coring
processing in the image signal processing system shown in FIG.
1;
[0026] FIG. 13 is a block diagram schematically showing one example
of an image signal processing system used for a general electronic
camera;
[0027] FIG. 14 is a block diagram schematically showing another
example of the image signal processing system used for the general
digital camera;
[0028] FIG. 15 is a diagram showing a processing result of the edge
emphasis processing in the image signal processing system shown in
FIG. 13;
[0029] FIG. 16 is a diagram showing s setting value of the coring
threshold level in the image signal processing system shown in FIG.
13;
[0030] FIG. 17 is a diagram showing a processing result of the
coring processing in the image signal processing system shown in
FIG. 13; and
[0031] FIG. 18 is a diagram showing a processing result of the
gamma correction processing in the image signal processing system
shown in FIG. 13.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0032] Hereinbelow, a description is given of an embodiment of the
present invention.
[0033] A description is given of the schematic structure of an
image signal processing system used for a general electronic camera
with reference to the drawings.
[0034] FIG. 13 is a block diagram schematically showing one example
of the image signal processing system used for the general
electronic camera.
[0035] The image signal processing system comprises: a solid image
pick-up device (CCD) 110 such as a CCD for receiving an optical
subject image formed through a photographing optical system (not
shown), for performing photoelectric conversion processing, and for
generating an image signal based on the subject image; a Y signal
generating unit 112 for receiving an output signal from the CCD
110, that is, an output signal through predetermined signal
processing, e.g., correlation double sampling processing, automatic
gain control processing, and analog/digital signal conversion
processing, and for extracting and generating a luminance signal
(hereinafter, referred to as a Y signal); a high-pass filter (HPF)
unit 113 for generating a contour signal (hereinafter, referred to
as an edge signal) which extracts a high-frequency component
(removes a low-frequency component) from the Y signal generated by
the Y signal generating unit 112; an edge emphasis changing unit
114 for multiplying a predetermined coefficient by the edge signal
generated by the HPF unit 113 and for generating the edge signal
having a changed edge emphasis; a coring unit 115 for generating
the edge signal having a high-band characteristic and a suppressed
noise component through coring processing by receiving the edge
signal having the edge emphasis changed by the edge emphasis
changing portion 114, by suppressing or removing the noise
component in the image, by improving an S/N ratio (signal/noise
ratio), and by thus generating a predetermined edge signal; an
adder 116 for generating the Y signal with a wide-band
characteristic and edge emphasis by adding the high-band Y signal
generated by the coring unit 115 and the Y signal generated by the
Y signal generating unit 112; a gamma correcting (Y.gamma.) unit
111 for generating the final Y signal by receiving the Y signal
with the wide band generated and outputted by the adder 116 and by
performing gamma (y) correction processing; a synchronization and
color correcting unit 121 for performing predetermined
synchronization processing so as to extract color signals
(hereinafter, referred to as C signals including an R signal, a G
signal, and a B signal) based on the output signal from the CCD 110
and for performing predetermined color correction processing; a
low-pass filter (LPF) unit 122 for limiting the band for generating
color signals (including an RL signal, a GL signal, and a BL
signal) obtained by extracting the low-frequency component
(removing the high-frequency component) from the color signals
(including the R signal, G signal, and B signal) subjected to the
synchronization and color correction processing by the
synchronization and color correcting unit 121; a color gamma
correcting unit (RGB.gamma. unit) 123 which subjects the color
signals (including the RL signal, the GL signal, and the BL signal)
generated by the LPF unit 122 to gamma correction processing; a
CrCb generating unit 124 for finally generating chroma signals (a
Cr signal and a Cb signal) with a preferable S/N ratio based on
color signals (including a .gamma.RL signal, a .gamma.GL signal,
and a .gamma.BL signal) subjected to color gamma correction
processing by the RGB.gamma. unit 123; and a JPEG compressing unit
131 for generating the image signal having JPEG compressing data by
the chroma signal (including the Cr signal and Cb signal) generated
by the CrCb generating unit 124 and by the Y signal generated by
the Y.gamma. unit 111, and for outputting the generated image
signal to a recording unit (not shown) for recording the image.
[0036] FIG. 14 is a block diagram showing another example of the
image signal processing system used for the conventional and
general electronic camera.
[0037] Referring to the other example shown in FIG. 14, the
structure of the image signal processing system is the same as that
of the electronic camera disclosed in Japanese Unexamined Patent
Application Publication No. 11-112837.
[0038] The image signal processing system of the other example
shown in FIG. 14 is substantially the same structure as that in the
one shown in FIG. 13 and, however, the processing for generating
the Y signal is different.
[0039] That is, the image signal processing system shown in FIG. 14
comprises: a solid image pick-up device (CCD) 110 such as a CCD
which receives an optical subject image formed by a photographing
optical system (not shown) and is subjected to the photoelectric
conversion processing, and which generates an image signal based on
the subject image; a gamma correcting (Y.gamma.) unit 111 which
receives an output signal from the CCD 110, namely, the output
signal through predetermined signal processing such as the
correlation double sampling processing, the automatic gain control
processing, and the analog/digital signal conversion processing and
which subjects the luminance signal (Y signal) to the gamma
correction processing; a Y signal generating unit 112 which
receives the output signal from the Y.gamma. unit 111 and which
extracts and generates the Y signal; a high-pass filter (HPF) unit
113 which generates an edge signal from the Y signal generated by
the Y signal generating unit 112; an edge emphasis changing unit
114 which generates the edge signal obtained by changing the edge
emphasis of the edge signal generated by the HPF unit 113; a coring
unit 115 which receives the edge signal generated by the edge
emphasis changing unit 114, subjects the edge signal to coring
processing, and generates the edge signal with a high-band
characteristic and a suppressed noise component; a synchronization
and color correcting unit 121 which performs predetermined
synchronization processing based on the output signal from the CCD
110 and performs predetermined color correction processing; a
low-pass filter (LPF) unit 122 for limiting the band which
generates color signals (including an RL signal, a GL signal, and a
BL signal) obtained by extracting a low-frequency component
(removing the high-frequency component) from the color signals
(including an R signal, a G signal, and a B signal) subjected to
the synchronization and color correction processing by the
synchronization and color correcting portion 121; a color gamma
correcting unit (RGB.gamma. unit) 123 which subjects the color
signals (including the RL signal, the GL signal, and the BL signal)
generated by the LPF unit 122 to gamma correction processing; a
YCrCb generating unit 125 for generating the color signals with a
preferable S/N ratio including the low-band Y signal based on color
signals (including a .gamma.RL signal, a .gamma.GL signal, and a
.gamma.BL signal) subjected to color gamma correction processing by
the RGB.gamma. unit 123; an adder 116 for generating the wide-band
Y signal with a wide-band characteristic by adding the low-band Y
signal generated by the YCrCb generating unit 125 and the high-band
Y signal generated by the coring unit 115; and a JPEG compressing
unit 131 for generating the image signal having JPEG compressing
data by the wide-band Y signal generated and outputted by the adder
116 and the chroma signal (including the Cr signal and Cb signal)
in the YCrCb signal generated by the YCrCb generating unit 125 and
for outputting the generated image signal to a recording unit (not
shown) for recording the image.
[0040] Briefly, in the other example shown in FIG. 14, the image
signal processing system comprises two distinct signal processing
systems: a signal processing system for generating the high-band Y
signal (edge signal) subjected to the edge emphasis processing and
a signal processing system for generating the low-band Y signal. A
desired wide-band Y signal is generated by adding the high-band Y
signal and the low-band Y signal which are generated by the
respective signal processing systems. In this case, the low-band Y
signal is generated together with the chroma signal in the signal
processing system for a color-system signal.
[0041] However, in the examples of the above-mentioned conventional
image signal processing systems shown in FIGS. 13 and 14, there is
a problem that a desired Y signal is not obtained.
[0042] That is, in the example of the conventional general image
signal processing system shown in FIG. 13, a signal processing
system using the Y signal (the processing in from the Y signal
generating unit 112 to the Y.gamma. unit 111) executes the gamma
correction processing (Y.gamma. unit 111) of the Y signal after
generating the Y signal.
[0043] On the other hand, in the one example shown in FIG. 13, the
CrCb generating unit 124 in the chroma signal processing system
(the processing in from the synchronization and color correcting
unit 121 to the CrCb generating unit 124) generally executes the
following processing. Namely, the RGB.gamma. unit 123 first
generates a predetermined Y signal based on the .gamma.RL signal,
the .gamma.GL signal, and the .gamma.BL signal which are subjected
to the color gamma correction processing by the RGB.gamma. unit
123. Herein, the Y signal is calculated based on a general
calculating formula (1).
[0044] [Formula 1]
Y=0.3R+0.59G+0.11B (1)
[0045] The Cr signal is generated by subtracting the Y signal
calculated by the above formula (1) from the .gamma.RL signal. The
Cb signal is generated by subtracting the Y signal calculated by
the above formula (1) from the .gamma.BL signal.
[0046] In other words, the Y signal is generated as mentioned above
in the processing for generating the Cr signal and the Cb signal.
However, the Y signal is generated based on the signal through the
gamma correction processing of the RGB.gamma. unit 123 as shown in
FIG. 13.
[0047] Therefore, in the example shown in FIG. 13, the Y signal
processing system performs the gamma correction processing in the
final stage of the processing. On the other hand, the chroma signal
processing system performs the processing for generating the chroma
signal (C signal) based on the signal through the gamma correction
processing. The foregoing includes a problem that a contradiction
is caused in the calculating result.
[0048] Further, in the one example shown in FIG. 13, the Y signal
is subjected to the gamma correction processing (Y.gamma. unit 111)
based on the signal through the coring processing. This case
includes the following problem.
[0049] In other words, in the one example of the image signal
processing system shown in FIG. 13, the edge emphasis processing is
executed by the HPF unit 113. A processing result of the edge
emphasis processing is indicated in FIG. 15.
[0050] FIG. 15 is a diagram showing the processing result of the
edge emphasis processing in the example of the image signal
processing system shown in FIG. 13. Referring to FIG. 15, the axis
of ordinate denotes the amount of noise and the axis of abscissa
denotes the amount of incident light, namely, the brightness of the
image.
[0051] In general, a noise component in the image signal generated
by the image pick-up device such as the CCD mainly includes,
so-called shot noise. Thus, as the amount of incident light
increases, the amount of noise included in the image signal
increases.
[0052] Upon executing the edge emphasis processing for extracting
the edge component from the above image signal, the noise component
is extracted as the edge component. Referring to FIG. 15, it is
understood that the amount of noise included in the entire image
signals after the edge emphasis processing is increased as compared
with the image signal before the processing. Since the amount of
noise increases as the luminance is higher, a larger edge-component
is extracted in a higher-luminance area due to this.
[0053] Sequentially, the coring processing is executed based on the
signal after the edge emphasis processing. In the coring
processing, the S/N ratio is improved by suppressing the noise
component of the edge signal.
[0054] FIG. 16 is a diagram showing a setting value of a coring
threshold level in the example of the image signal processing
system shown in FIG. 13. Referring to FIG. 16, the axis of ordinate
denotes the amount of noise and the axis of abscissa denotes the
amount of incident light, namely, the brightness of the image.
[0055] In the system shown in the example of FIG. 13, the coring
threshold level is set as shown by a dotted line in FIG. 16. In
this case, when an intersection a is formed by a coring threshold
level .vertline.a.vertline. and a line segment A indicating the
image signal, the noise component is not emphasized in a range B as
a low-luminance area of the intersection a and the noise component
remains in a range C as a high-luminance area of the intersection
a.
[0056] As a result, the signal subjected to the coring processing
is generated, containing the signal having the noise component as
shown in FIG. 17.
[0057] FIG. 17 is a diagram showing the processing result of the
coring processing in the example of the image signal processing
system in the one example shown in FIG. 13. Referring to FIG. 17,
the axis of ordinate denotes the amount of noise and the axis of
abscissa denotes the amount of incident light (brightness of the
image).
[0058] The signal generated through the above coring processing is
subjected to the gamma correction processing.
[0059] FIG. 18 is a diagram showing the processing result of the
gamma correction processing in the example of the image signal
processing system shown in FIG. 13.
[0060] Referring to FIG. 18, a gamma characteristic curve is slowly
inclined. Therefore, as the luminance is higher, the signal is
compressed. Thus, the noise component is suppressed at a portion
near the high luminance. However, the predetermined amount of noise
component remains in the finally generated image signal.
[0061] The complete suppression of the noise component needs the
increase of the setting of the coring threshold level. In this
case, not only the noise component but also the original
high-frequency component is removed.
[0062] That is, when the edge component of the target signal is
subjected to the coring processing, the coring threshold level is
set to a high value so as to remove the noise component in the
high-luminance area of the image and then the edge signal in the
low-luminance area is removed together with the noise component as
a result of the coring processing. As a consequence, this becomes a
factor that the resolution of the image is insufficient in the
low-luminance area. It is not preferable means for setting the
coring threshold level to an unnecessary level in views of
generating the preferable image data.
[0063] When the coring threshold level is set to be low so as to
let the edge component remain in the low-luminance area as much as
possible, the noise component in the high-luminance area is not
sufficiently removed by the coring processing. Therefore, there is
a problem that the noise component remains in the image signal
generated by this.
[0064] In the conventional general image signal processing system
as the example as shown in FIG. 14, when desired chroma signal and
Y signal are generated based on the output signal from the CCD 110,
the chroma signal and the low-band Y signal are generated by
performing the same processing of the same processing system.
Therefore, signal processing for generating the low-band Y signal
and the chroma signal is performed based on the signal subjected to
the band limitation using the same LPF 122.
[0065] In general, upon the chroma signal generation processing,
the band limitation is largely performed in the band limitation
processing of the LPF 122 so as to mainly reduce the unnecessary
noise component. Thus, the advantage for reducing the noise is
obtained. It is necessary to limit the band by the LPF 122 as much
as at the low level so as to obtain the Y signal with the wider
band.
[0066] In the conventional image signal processing system shown in
FIG. 14, the band is largely limited in the band limitation
processing of the LPF 122 in consideration of generating the chroma
signal with the preferable S/N ratio. Then, the band of the
simultaneously generated low-band Y signal is narrower than the
desired band.
[0067] When the band is largely limited by the LPF 122 in
consideration of generating the low-band Y signal in the wide band,
an unnecessary noise component is not removed from the chroma
signal which is simultaneously generated. Therefore, the desired
chroma signal, namely, the chroma signal with the preferable S/N
ratio is not generated.
[0068] As mentioned above, it is not easy to generate the chroma
signal with the preferable S/N ratio and to generate the Y signal
in the wide band by performing the same processing by the same
processing system.
[0069] The present invention is devised in views of the
above-mentioned points and embodiment is described hereinlater.
[0070] FIG. 1 is a block diagram schematically showing an image
signal processing system used for a camera according to an
embodiment of the present invention. According to the embodiment of
the present invention, the image signal processing system is used
for an electronic camera system as an example.
[0071] Referring to FIG. 1, the image signal processing system of
the electronic camera comprises: a solid image pick-up device (CCD)
10 such as a CCD for receiving an optical subject image formed
through a photographing optical system (not shown), for performing
photoelectric conversion processing, and for generating an image
signal based on the subject image; a gamma correcting unit
(Y.gamma. unit) 11, as first y correction processing means, for
receiving an output signal (color image signal) through
predetermined signal processing such as correlation double sampling
processing, automatic gain control processing, and analog/digital
signal conversion processing and for performing gamma correction
processing (of the luminance signal); a Y signal generating unit
12, as luminance signal generating means, for receiving the image
signal through the gamma correction processing in the Y.gamma. unit
11, and for extracting and generating the Y signal (luminance
signal); a high-pass filter (HPF) unit 13, as a part of edge
emphasis processing means and band limiting means, for generating a
contour signal (edge signal) which extracts a high-frequency
component (removes a low-frequency component) from the Y signal
generated by the Y signal generating unit 12; an edge emphasis
changing unit 14, as a part of edge emphasis changing means, for
multiplying a predetermined coefficient by the edge signal
generated by the HPF unit 13 and for generating the edge signal
having a changed edge emphasis; a coring unit 15, as coring
processing means, for generating a predetermined edge signal having
a high-band characteristic and a suppressed noise component through
coring processing by receiving the edge signal having the edge
emphasis changed by the edge emphasis changing portion 14, by
suppressing or removing the noise component in the image, by
improving an S/N ratio (signal/noise ratio), and by thus generating
a predetermined edge signal; an adder 16 for generating the Y
signal with the wide-band characteristic and edge emphasis by
adding the signal generated by the coring unit 15 and the Y signal
generated by the Y signal generating unit 12; a synchronization and
color correcting unit 21, as color correction processing means, for
performing predetermined synchronization processing so as to
extract R signal, G signal, and B signal based on the output signal
from the CCD 10 and for performing predetermined color correction
processing; a low-pass filter (LPF) unit 22 for limiting the band,
as band limiting means, for generating signals (including an RL
signal, a GL signal, and a BL signal) obtained by extracting the
low-frequency component (removing the high-frequency component)
from the signals including the R signal, G signal, and B signal
subjected to the synchronization and color correction processing by
the synchronization and color correcting portion 21; a color gamma
correcting unit (RGB.gamma. unit) 23, as second gamma correction
processing means, for performing the gamma correction processing of
the signals including the RL signal, the GL signal, and the BL
signal generated by the LPF unit 22; a CrCb generating unit 24, as
chroma signal generating means, for finally generating a C signal,
a Cr signal, and a Cb signal with a preferable S/N ratio based on
color signals including a .gamma.RL signal, a .gamma.GL signal, and
a .gamma.BL signal subjected to color gamma correction processing
by the RGB.gamma. unit 23; and a JPEG compressing unit 31 for
generating the image signal having JPEG compressing data by the
chroma signal including the Cr signal and Cb signal generated by
the CrCb generating unit 24 and by the wide-band Y signal generated
and outputted by the adder 16 and for outputting the generated
image signal to a recording unit (not shown) for recording the
image.
[0072] As mentioned above, the image signal processing system
according to the embodiment comprises different processing systems,
a first signal processing system and a second signal processing
system. The first signal processing system comprises a signal
processing system contributing to the generation of, mainly, the
luminance signal (hereinafter, referred to as the Y signal), that
is, a luminance signal processing system, including the first gamma
correction processing means (Y.gamma. unit 11) which performs the
gamma correction processing of the output from the image pick-up
device (CCD 10) and the luminance signal generating means (Y signal
generating unit 12) which generates a luminance-system signal based
on the output of the first gamma correction processing means
(Y.gamma. unit 11). The second signal processing system
contributing to the generation of, mainly, the chroma signal (C
signal), that is, a chroma signal processing system including the
chroma signal generating means (CrCb generating unit 24) which
generates a color-system signal based on the output from the image
pick-up device (CCD 10) that is not subjected to the gamma
correction processing.
[0073] The first signal processing system (luminance signal
processing system) comprises the edge emphasis processing means
(the HPF unit 13 and the edge emphasis changing unit 14) and the
coring processing means (coring unit 15) at the rear stage of the
luminance signal generating means (Y signal generating unit
12).
[0074] The second signal processing system (chroma signal
processing system) comprises the color correction means
(synchronization and color correction unit 21) for performing the
color correction processing and the second gamma correction
processing means (RGB.gamma. unit 23) for performing the gamma
correction processing at the front stage of the chroma signal
generating means (CrCb generating unit 24) such that the both means
functions in the above-mentioned order.
[0075] Further, the second signal processing system (color-system
signal processing system) comprises the band limiting means (LPF
unit 22) independently of the first signal processing system
(luminance signal processing system). Incidentally, the second
signal processing system may be constructed so as to generate not
only the chroma signal (Cr signal and Cb signal) but also a color
difference signal or a signal obtained by linearly converting the
color difference signal, such as I signal and Q signal or U signal
and V signal, as the color-system signal.
[0076] Here, the luminance signal processing system is described in
detail.
[0077] The CCD 10 comprises predetermined-type color filters (also
referred to as color filters). The color filters have RGB bayer
alignments as shown in FIG. 2.
[0078] FIG. 2 is a diagram showing the alignment of color filter
arrays arranged in front of the CCD 10 in the electronic camera
according to the embodiment. Referring to FIG. 2, the configuration
(coordinates) of the output signal from the CCD 10 is shown.
[0079] The Y.gamma. unit 11 comprises a predetermined input end
portion (not shown) for receiving the output signal from the CCD 10
or a color image signal substantially equivalent to the output
signal.
[0080] The Y.gamma. unit 11 receives input data (refer to FIG. 2)
which is supplied from the CCD 10 via the input end portion,
subjects the input data to predetermined gamma correction
processing, and generates a non-linear output signal.
[0081] The gamma correction processing is a signal processing by
which the reproduced image (display image) obtains accurate
gradation characteristics on the display screen of display means
for displaying the image based on the generated image data. The
gamma characteristic of a CRT (Cathode Ray Tube, so-called Braun
tube) as general display means is 2.22. A gamma correcting
coefficient used for the gamma correction processing is as follows.
1 = 1 / 2.22 0.45
[0082] Therefore, the correction is performed so as to obtain the
above value in the gamma correction processing.
[0083] FIG. 3 is a diagram showing the concept of the gamma
correction processing of the Y.gamma. unit 11 in the image signal
processing system according to the embodiment.
[0084] In the RGB.gamma. unit 23 in the chroma signal processing
system, which will be described later, the similar color gamma
correction processing is performed.
[0085] The Y signal generating unit 12 receives the output signal
from the Y.gamma. unit 11 and generates a predetermined luminance
signal (Y signal). According to the embodiment, the luminance
signal (Y signal) is generated from the RGB signals based on the
following general calculating formula (1).
[0086] [Formula 1]
Y=0.3R+0.59G+0.11B (1)
[0087] FIG. 4 is a diagram showing coordinates of the luminance
signal corresponding to the CCD output signal shown in FIG. 2.
[0088] The luminance signal of a coordinate Y(0, 0) in FIG. 4 is
calculated by using the above formula (1), thereby obtaining the
following formula (2). 2 [ Formula 2 ] Y ( 0 , 0 ) = [ R ( 0 , 0 )
G r ( 1 , 0 ) G b ( 0 , 1 ) B ( 1 , 1 ) ] ( 0.3 0.295 0.295 0.11 )
( 2 )
[0089] As mentioned above, the coordinate Y(0, 0) is generated
based on four pixel signals from the CCD output signals shown in
FIG. 2. That is, the four pixel signals are
[0090] R(0, 0),
[0091] Gr(1, 0)
[0092] Gb(0, 1) and
[0093] B(1, 1).
[0094] The luminance signal of the coordinate Y(1, 0) in FIG. 4 is,
as well, calculated by using the above formula (1), thereby
obtaining the following formula (3). 3 [ Formula 3 ] Y ( 1 , 0 ) =
[ G r ( 1 , 0 ) R ( 2 , 0 ) B ( 1 , 1 ) G b ( 2 , 1 ) ] ( 0.295 0.3
0.11 0.295 ) ( 3 )
[0095] The coordinate Y(1, 0) is generated based on four pixel
signals. That is, the four pixel signals are
[0096] Gr(1, 0),
[0097] R(2, 0),
[0098] B(1, 1), and
[0099] Gb(2, 1).
[0100] The Y signal is similarly generated based on all the output
signals from the CCD 10.
[0101] When generating the Y signal, the calculation using the
formula (1) is performed based on the four pixel signals as
mentioned above.
[0102] Here, the G signal includes two pixel signals of the Gr
signal and Gb signal. In the formula (1), 0.59 is multiplied to the
G signal. Thus, 0.295 (=(0.59/2)) is multiplied to the Gr signal
and the Gb signal respectively.
[0103] The edge extracting HPF unit 13 generates an edge signal
Edge (x, y) by multiplying the spatial filter (HPF) for extracting
the edge to the Y signal generated by the Y signal generating unit
12 as shown in FIG. 5.
[0104] FIG. 5 is a diagram showing the HPF coefficient of the
spatial filter (HPF) for extracting the edge in the image signal
processing system according to the embodiment.
[0105] The edge signal Edge (x, y) is calculated by using the
following formula (4) based on the Y signal having nine pixels and
the HPF coefficient shown in FIG. 5.
[0106] [Formula 4]
Edge(x, y)=.SIGMA.(Y(ij)*k(ij)) (4)
[0107] Specifically, the edge signal is generated by calculation
shown in the following formula (5). 4 [ Formula 5 ] Edge ( 1 , 1 )
= Y ( 0 , 0 ) * ( - 1 ) + Y ( 1 , 0 ) * 0 + Y ( 2 , 0 ) * ( - 1 ) +
Y ( 0 , 1 ) * 0 + Y ( 1 , 1 ) * 4 + Y ( 2 , 1 ) * 0 + Y ( 0 , 2 ) *
( - 1 ) + Y ( 1 , 2 ) * 0 + Y ( 2 , 2 ) * ( - 1 ) ( 5 )
[0108] The edge emphasis changing unit 14 executes the
predetermined edge emphasis changing processing of the generated
edge signal. Therefore, the coring unit 15 executes the coring
processing of the output signal.
[0109] FIG. 6 is a diagram showing the concept of the coring
processing in the image signal processing system according to the
embodiment.
[0110] In the coring processing according to the embodiment, the
output is suppressed and is set to zero in the case of a small
output signal within a range of input edge signals (-a) to a. That
is, the small output signal, typically for example, the noise, is
not subjected to the edge emphasis processing. Incidentally, in the
coring processing, different positive and negative values may be
set to the coring threshold level, that is, within the range of the
input edge signals (-a) to a.
[0111] The adder 16 adds the above-generated edge signal and the Y
signal generated by the Y signal generating unit 12, thereby
generating a predetermined wide-band Y signal.
[0112] Next, the detail description is given of the chroma signal
processing system.
[0113] FIG. 7 is a diagram showing the concept of the
synchronization processing in the image signal processing system
according to the embodiment.
[0114] The synchronization and color correcting unit 21 receives
input data (refer to input data shown in FIG. 7; exactly the same
as the input data shown in FIG. 2) of the output signal from the
CCD 10 or the color image signal substantially equivalent to the
output signal and performs the synchronization. The synchronization
processing is interpolation processing which is performed by
multiplying an (N.times.N) matrix shown in FIG. 7 to the input data
of the color image signal. Thus, three image signals, namely, Ri,
Gi, and Bi signals are generated.
[0115] Incidentally, in the electronic camera and its image signal
processing system, the synchronization processing is conventional
general-processing. Therefore, a detailed description thereof is
omitted.
[0116] Next, the Ri, Gi, and Bi signals generated by the
synchronization is subjected to the color correction processing.
The color correction processing is performed based on the
calculation shown in formulae (6), (7), and (8). In other words,
the chroma signal is corrected by multiplying predetermined
coefficients K1 to K9 to the chroma signal at the same
coordinate.
[0117] [Formula 6]
Ro(x, y)=K1*Ri(x, y)+K2*Gi(x, y)+K3*Bi(x, y) (6)
[0118] [Formula 7]
Go(x, y)=K4*Ri(x, y)+K5*Gi(x, y)+K6*Bi(x, y) (7)
[0119] [Formula 8]
Bo(x, y)=K7*Ri(x, y)+K8*Gi(x, y)+K9*Bi(x, y) (8)
[0120] Thus, color correcting signals Ro, Go, and Bo are generated
for the Ri, Gi, and Bi signals.
[0121] The color correction processing is generally put into
practical use in the conventional electronic camera and its image
signal processing system and therefore the detailed description
thereof is omitted.
[0122] The LPF unit 22 subjects to the band limitation processing,
the color-system signal subjected to the synchronization and the
color correction processing in the synchronization and the color
correcting unit 21. The band limitation processing is as the same
as the processing of the edge extracting HPF unit 13 in the above Y
signal processing system.
[0123] That is, the LPF unit 22 generates signals Rlpf, Glpf, and
Blpf which are subjected to the band limitation by multiplying the
spatial filter (LPF) used for limiting the band shown in FIG. 8 to
the chroma signal on which the synchronization and color correction
processing are performed.
[0124] FIG. 8 is a diagram showing the LPF coefficient of the
spatial filter (LPF) used for limiting the band in the image signal
processing system according to the embodiment.
[0125] For example, the band-limited signal Rlpf (x, y) is
calculated by using the following formula (9) based on the Ro
signal having nine pixels and the HPF coefficient shown in FIG.
8.
[0126] [Formula 9]
Rlpf(x, y)=.SIGMA.(Ro(ij)*L(ij))/.SIGMA.L(ij) (9)
[0127] Specifically, the band-limited signal Rlpf (x, y) is
generated by calculation shown in the following formula (12). 5 [
Formula 12 ] R1pf ( 1 , 1 ) = Ro ( 0 , 0 ) * 1 + Ro ( 1 , 0 ) * 2 +
Ro ( 2 , 0 ) * 1 + Ro ( 0 , 1 ) * 2 + Ro ( 1 , 1 ) * 4 + Ro ( 2 , 1
) * 2 + Ro ( 0 , 2 ) * 1 + Ro ( 1 , 2 ) * 2 + Ro ( 2 , 2 ) * 1 ( 12
)
[0128] Similarly, the band-limited signal Glpf (x, y) is calculated
by using the following formula (10) based on the Go signal having
nine pixels and the HPF coefficient shown in FIG. 8.
[0129] [Formula 10]
Glpf(x, y)=.SIGMA.(Go(ij)*L(ij))/.SIGMA.L(ij) (10)
[0130] Specifically, the band-limited signal Glpf (x, y) is
generated by calculation shown in the following formula (13). 6 [
Formula 13 ] G1pf ( 1 , 1 ) = Go ( 0 , 0 ) * 1 + Go ( 1 , 0 ) * 2 +
Go ( 2 , 0 ) * 1 + Go ( 0 , 1 ) * 2 + Go ( 1 , 1 ) * 4 + Go ( 2 , 1
) * 2 + Go ( 0 , 2 ) * 1 + Go ( 1 , 2 ) * 2 + Go ( 2 , 2 ) * 1 ( 13
)
[0131] Further, the band-limited signal Blpf (x, y) is calculated
by the following formula (11) based on the Bo signal having nine
pixels and the HPF coefficient shown in FIG. 8.
[0132] [Formula 11]
Blpf(x, y)=.SIGMA.(Bo(ij)*L(ij))/.SIGMA.L(ij) (11)
[0133] Specifically, the band-limited signal Blpf is generated by
the calculation shown in the following formula 14. 7 [ Formula 14 ]
B1pf ( 1 , 1 ) = Bo ( 0 , 0 ) * 1 + Bo ( 1 , 0 ) * 2 + Bo ( 2 , 0 )
* 1 + Bo ( 0 , 1 ) * 2 + Bo ( 1 , 1 ) * 4 + Bo ( 2 , 1 ) * 2 + Bo (
0 , 2 ) * 1 + Bo ( 1 , 2 ) * 2 + Bo ( 2 , 2 ) * 1 ( 14 )
[0134] The RGB.gamma. unit 23 executes the predetermined gamma
correction processing based on the above-generated and band-limited
signals Rlpf, Glpf, and Blpf. After that, the CrCb generating unit
24 executes the CrCb generation processing of the output
signals.
[0135] In the CrCb generation processing, the Y signals are
generated from the band-limited signals Rlpf, Glpf, and Blpf by
using the above formula (1) as shown in the following formula
(15).
[0136] [Formula 15]
Y(x, y)=0.3*Rlpf(x, y)+0.59*Glpf(x, y)+0.11*Blpf(x, y) (15)
[0137] The Cr signal is calculated by subtracting the Y signal
generated by the formula (15) from the signal Rlpf. That is, the Cr
signal is calculated as shown by the following formula (16).
[0138] [Formula 16]
Cr(x, y)=Rlpf(x, y)-Y(x, y) (16)
[0139] The Cb signal is calculated by subtracting the Y signal
generated by the above formula (15) from the signal Blpf. That is,
the Cb signal is calculated as shown by the following formula
(17).
[0140] [Formula 17]
Cb(x, y)=Blpf(x, y)-Y(x, y) (17)
[0141] The above-generated Cr signal and Cb signal become the
chroma signals C with a preferable S/N ratio.
[0142] Here, the embodiment will be described in views of a
relationship between the gamma correction processing of the Y
signal and the Y signal generation processing.
[0143] Table 1 shows the relationship between the gamma correction
processing of the Y signal and the Y signal generation processing,
and indicates processing in the image signal processing system
according to the embodiment and processing in the conventional
image signal processing system shown in FIG. 13.
1TABLE 1 1 2
[0144] Referring to Table 1, a column (A) shows a part of the
processing in the image signal processing system according to the
embodiment, and a column (B) shows a part of the image signal
processing system in the example shown in FIG. 13.
[0145] As mentioned above, in the image signal processing system
according to the embodiment, the output signal from the CCD 10 is
set to the input data and the Y signal of the input data is
subjected to the gamma correction processing. After that, the Y
signal generating unit 12 generates the Y signal based on the
processed signal (refer to FIG. 1).
[0146] On the other hand, in the conventional image signal
processing system shown in FIG. 13, the Y signal is generated and
thereafter the gamma correction processing is performed.
[0147] A specific description is given of the difference between
the image signal processing system according to the embodiment and
the conventional image signal processing system shown in FIG. 13
with reference to Table 1.
[0148] For example, when the output signal from the CCD (10, 110)
or the color image signal equivalent to the output signal has the
following values:
[0149] R signal=100,
[0150] G signal=0, and
[0151] B signal=0,
[0152] through the Y signal generation processing and the gamma
correction processing by both the systems, the calculating results
are different as follows.
[0153] First, in the conventional image signal processing system
shown in FIG. 13, the calculating result is obtained as shown in
the column (B) in Table 1.
[0154] In other words, in the conventional image signal processing
system shown in FIG. 13, the output signal (color image signal)
from the CCD 110 is received and the predetermined Y signal
generation processing is performed. Here, the Y signal generation
processing is performed based on the following formula (1).
[0155] [Formula 1]
Y=0.3R+0.59G+0.11B (1)
[0156] Therefore, the processing result of the Y signal generating
unit 112 is shown in the column (B) in Table 1. That is, 8 Y = 0.3
.times. 100 + 0.59 .times. 0 + 0.11 .times. 0 = 30
[0157] The thus-generated Y signal (=30) is subjected to the
predetermined signal processing as mentioned above with reference
to FIG. 13. Then, the Y.gamma. unit 111 finally performs the gamma
correction processing. In this case, the gamma correction
processing is obtained by the following formula as shown in the
column (B) in Table 1.
Out=((In/255){circumflex over ( )}0.45).times.255
[0158] Here, symbol Out denotes the output signal and symbol In
denotes the input signal. In this case, the input signal In
corresponds to the Y signal which is generated by the above formula
(1) and is thereafter subjected to various signal processing. It is
assumed that the gamma correcting coefficient .gamma. is equal to
0.45. Therefore, the processing result in the Y.gamma. unit 111 is
as follows. 9 Out = ( ( In / 255 ) ^ 0.45 ) .times. 255 = ( ( 30 /
255 ) ^ 0.45 ) .times. 255 97
[0159] Here, symbol {circumflex over ( )} denotes the power. That
is, the Y signal (=97) finally outputted is obtained.
[0160] On the contrary, in the image signal processing system
according to the embodiment, the output signal from the CCD 10 or
the color image signal equivalent to the output signal has the
following values:
[0161] R signal=100,
[0162] G signal=0, and
[0163] B signal=0,
[0164] through the gamma correction processing and the Y signal
generation processing, the calculating result is obtained as shown
by the column (A) in Table 1.
[0165] In the image signal processing system according to the
embodiment, as shown in FIG. 1, the output signal (color image
signal) is received from the CCD 10 and the Y.gamma. unit 11 first
executes the gamma correction processing. In this case, the gamma
correction processing is obtained by the following formula as shown
by the column (A) in Table 1.
Out=((In/255){circumflex over ( )}0.45).times.255
[0166] Here, symbol Out denotes the output signal and symbol In
denotes the input signal. In this case, the input signal In
corresponds to the Y signal which is generated by the above formula
(1) and is thereafter subjected to various signal processing. It is
assumed that the gamma correcting coefficient .gamma. is equal to
0.45. Therefore, the processing result in the Y.gamma. unit 111 is
as follows. 10 Out = ( ( In / 255 ) ^ 0.45 ) .times. 255 = ( ( 100
/ 255 ) ^ 0.45 ) .times. 255 167
[0167] Here, symbol {circumflex over ( )} denotes the power. That
is, the color image signal is generated with
[0168] R signal=167,
[0169] G signal=0, and
[0170] B signal=0.
[0171] The generated color image signal is subjected to the Y
signal generation processing. The Y signal generation processing is
based on the following formula (1).
[0172] [Formula 1]
Y=0.3R+0.59G+0.11B (1)
[0173] Hence, the processing result of the Y signal generating unit
12 is shown in the column (A) in Table 1. That is, 11 Y = 0.3
.times. 167 + 0.59 .times. 0 + 0.11 .times. 0 = 50
[0174] That is, the Y signal (=50) finally outputted is
obtained.
[0175] As mentioned above, the generated Y signal has varied values
depending on whether the gamma correction processing is performed
before the Y signal generation processing or after that.
[0176] In both the image signal processing system according to the
embodiment and the conventional one shown in FIG. 13, the same
processing is implemented in the chroma signal processing system.
In this case, the CrCb generating units 24 and 124 implement the
CrCb generation processing based on the signal after the gamma
correction processing of the RGB.gamma. units 23 and 123 are
respectively performed.
[0177] As mentioned above, the Y signal is generated in the CrCb
generation processing. However, the same Y signal as that in the
above Y signal processing system must be used.
[0178] However, in the example shown in FIG. 13, the latter stage
portion performs the gamma correction processing in the Y signal
processing system and the chroma signal is generated by the Y
signal which is generated based on the signal after the gamma
correction processing in the color-system signal processing system.
Hence, as mentioned above with reference to Table 1, the Y signal
(Y=97 in the column (B) of Table 1) in the Y signal processing
system is different from the Y signal (Y=50 in the column (A) of
Table 1) in the color-system signal processing system.
[0179] On the other hand, in the image signal processing system
according to the embodiment, the Y signal in the Y signal
processing system is substantially the same as the Y signal in the
color-system signal processing system.
[0180] Namely, in the image signal processing system according to
the embodiment, the Y signal in the Y signal processing system is
subjected to the Y signal generation processing based on the signal
after the gamma correction processing as mentioned above (refer to
FIG. 1). The generated Y signal has a value of 50 as shown in the
column (A) of Table 1.
[0181] In the image signal processing system according to the
embodiment, the Y signal in the color-system signal processing
system, in other words, the Y signal used for generating the chroma
signal in the CrCb generation processing is generated based on the
signal after the gamma correction processing in the RGB.gamma. unit
23 at the front stage of the CrCb generating unit 24 (refer to FIG.
1). The generated Y signal has a value of 50 as shown in the column
(A) of Table 1.
[0182] As described above, in the image signal processing system
according to the embodiment, the Y signal generated in the Y signal
processing system is substantially the same as the Y signal used
for generating the chroma signal in the color signal processing
system. Thus, no contradiction exists between the Y signal and the
chroma signal which are generated in the image signal processing
system according to the embodiment and the correct color
reproduction is always realized.
[0183] Next, a description is given of the embodiment in views of a
relationship between the gamma correction processing and the color
correction processing of the chroma signal.
[0184] Table 2 shows the relationship between the gamma correction
processing and the color correction processing of the chroma signal
and indicates the processing in the image signal processing system
according to the embodiment and the processing in the conventional
image signal processing system.
2TABLE 2 3 4
[0185] Referring to Table 2, a column (A) shows a part of the
processing in the image signal processing system according to the
embodiment, and a column (B) shows a part of the conventional image
signal processing system.
[0186] As mentioned above, in the image signal processing system
according to the embodiment, the output signal from the CCD 10 is
set to the input data and the synchronization and color correction
processing unit 21 subjects the input data to the synchronization
processing and the color correction processing. After that, the
RGB.gamma. unit 23 subjects the color-system signal to the .gamma.
correction processing (refer to FIG. 1 and the column (A) in Table
2).
[0187] On the other hand, in the conventional image signal
processing system, as disclosed in Japanese Unexamined Patent
Application Publication No. 9-130816, the color-system signal is
subjected to the gamma correction processing and thereafter the
color correction processing is performed based on the generated
signal through the gamma correction processing (refer to the column
(B) in Table 2).
[0188] A specific description is given of the difference between
the image signal processing system according to the embodiment and
the conventional image signal processing system with reference to
Table 2.
[0189] For example, when the output signal from the CCD (10, 110)
or the color image signal equivalent to the output signal has the
following values
[0190] R signal=100,
[0191] G signal=20, and
[0192] B signal=30,
[0193] and the gamma correction processing and the color correction
processing are performed by both the systems.
[0194] First, in the conventional image signal processing system,
the calculating result is obtained as shown in the column (B) in
Table 2.
[0195] In other words, in the conventional image signal processing
system, the output signal (color image signal) from the CCD 110 is
received and the predetermined gamma correction processing is
performed. Here, the gamma correction processing is performed based
on the following formula as shown in the column (B) in Table 2.
Out=((In/255){circumflex over ( )}0.45).times.255
[0196] Here, symbol Out denotes the output signal and symbol In
denotes the input signal. In this case, the input signal In
corresponds to the output signal (color image signal) from the CCD
110. It is assumed that the gamma correcting coefficient .gamma. is
equal to 0.45. Here, symbol {circumflex over ( )} denotes the
power. Therefore, the processing result of the gamma correction
processing is as follows. 12 Out ( R ) = ( ( In ( R ) / 255 ) ^
0.45 ) .times. 255 = ( ( 100 / 255 ) ^ 0.45 ) .times. 255 167 Out (
G ) = ( ( In ( G ) / 255 ) ^ 0.45 ) .times. 255 = ( ( 20 / 255 ) ^
0.45 ) .times. 255 81 Out ( B ) = ( ( In ( B ) / 255 ) ^ 0.45 )
.times. 255 = ( ( 30 / 255 ) ^ 0.45 ) .times. 255 97
[0197] Hence, the processing result of the gamma correction
processing is as shown in the column (B) in Table 2, that is,
[0198] R signal=167,
[0199] G signal=81, and
[0200] B signal=97.
[0201] The thus-generated chroma signal is subjected to the color
correction processing. Here, the color correction processing is
performed by using the above-stated formulae (6) to (8) as shown in
the column (B) in Table 2 (refer to FIG. 7). Here, coefficients K1
to K9 are set as follows.
[0202] That is,
[0203] K1=1.2
[0204] K2=-0.1
[0205] K3=-0.1
[0206] K4=-0.1
[0207] K5=-1.2
[0208] K6=-0.1
[0209] K7=-0.1
[0210] K8=-0.1, and
[0211] K9=1.2
[0212] This enables the acquisition of synchronized signals
(further, color-corrected signals) for generating the chroma
signals having 13 R = 1.2 .times. 167 - 0.1 .times. 81 - 0.1
.times. 97 183 , G = - 0.1 .times. 167 + 1.2 .times. 81 - 0.1
.times. 97 71 , and B = - 0.1 .times. 167 - 0.1 .times. 81 + 1.2
.times. 97 92
[0213] The image is reproduced and displayed based on the
above-generated image data by using display means having a
characteristic of a display luminance for a predetermined
non-linear input. Upon this display operation, the non-linear
characteristic is offset against the non-linear characteristic
which is previously given to the signal supplied to the display
means, thereby performing the proper display operation. The
characteristic of the display means is de-gamma (de.gamma.)
characteristic. The de-gamma characteristic is indicated by the
following formula shown in the column (B) in Table 2.
Out=((In/255){circumflex over ( )}2.22).times.255
[0214] Here, symbol Out denotes the output signal and symbol In
denotes the input signal. In this case, the input signal In
corresponds to the color image signal including the color signal
through the color correction processing. It is assumed that a
de-gamma correcting coefficient de.gamma. is equal to 2.22 which is
a reciprocal of the gamma correcting coefficient .gamma. (=0.45).
Here, symbol {circumflex over ( )} denotes the power. Therefore,
the display characteristic of the display means is as follows by
the de-gamma characteristic. 14 Out ( R ) = ( ( In ( R ) / 255 ) ^
2.22 ) .times. 255 = ( ( 183 / 255 ) ^ 2.22 ) .times. 255 122 Out (
G ) = ( ( In ( G ) / 255 ) ^ 2.22 ) .times. 255 = ( ( 71 / 255 ) ^
2.22 ) .times. 255 15 Out ( B ) = ( ( In ( B ) / 255 ) ^ 2.22 )
.times. 255 = ( ( 92 / 255 ) ^ 2.22 ) .times. 255 26
[0215] Hence, the processing result of the gamma correction
processing is, as shown in the column (B) in Table 2,
[0216] R signal=122,
[0217] G signal=15, and
[0218] B signal=26.
[0219] As will be understood, the signal under the influence of the
de-gamma characteristic is different from the signal of the
color-system after the gamma correction processing.
[0220] That is, in the conventional image signal processing system,
the signal after the gamma correction processing is subjected to
the color correction processing upon generating the image data.
When the image is reproduced and displayed based on the
thus-generated image data, the color reproductionability is not
realized with accuracy.
[0221] On the contrary, in the image signal processing system
according to the embodiment, when the output signal from the CCD 10
or the color image signal equivalent to the output signal has the
following values
[0222] R signal=100,
[0223] G signal=20, and
[0224] B signal=30,
[0225] and the gamma correction processing and the color correction
processing are performed. Then, the calculating result is obtained
as shown in the column (A) in Table 2.
[0226] In other words, in the image signal processing system
according to the embodiment, as shown in FIG. 1, the output signal
(color image signal) from the CCD 10 is received and the
synchronization and color correction processing is performed. Here,
the color correction processing is performed based on the
above-stated formulae (6) to (8) as shown in the column (A) in
Table 2, similarly to the above conventional system (refer to FIG.
7). Coefficients K1 to K9 set here are the same as those in the
conventional image signal processing system. Hence, the following
signals are generated, that is, 15 R = 1.2 .times. 100 - 0.1
.times. 20 - 0.1 .times. 30 115 G = - 0.1 .times. 100 + 1.2 .times.
20 - 0.1 .times. 30 11 , and B = - 0.1 .times. 100 - 0.1 .times. 20
+ 1.2 .times. 30 24.
[0227] The RGB.gamma. unit 23 subjects the above-generated
color-system signal to the gamma correction processing. In this
case, the gamma correction processing is obtained by the following
formula as shown in the column (A) in Table 2.
Out=((In/255){circumflex over ( )}0.45).times.255
[0228] Here, symbol Out denotes the output signal and symbol In
denotes the input signal. In this case, the input signal In
corresponds to the signal generated through the above color
correction processing (color image signal). It is assumed that the
gamma correcting coefficient .gamma. is equal to 0.45. Here, symbol
{circumflex over ( )} denotes the power. That is, the gamma
correction processing is similar to that in the conventional image
signal processing system.
[0229] In the image signal processing system according to the
embodiment, the processing result of the gamma correction
processing is as follows. 16 Out ( R ) = ( ( In ( R ) / 255 ) ^
0.45 ) .times. 255 = ( ( 115 / 255 ) ^ 0.45 ) .times. 255 178 Out (
G ) = ( ( In ( G ) / 255 ) ^ 0.45 ) .times. 255 = ( ( 11 / 255 ) ^
0.45 ) .times. 255 62 Out ( B ) = ( ( In ( B ) / 255 ) ^ 0.45 )
.times. 255 = ( ( 24 / 255 ) ^ 0.45 ) .times. 255 88
[0230] Hence, the processing result of the gamma correction
processing is, as shown in the column (A) in Table 2,
[0231] R signal=178,
[0232] G signal=62, and
[0233] B signal=88.
[0234] When reproducing and displaying the optimal-form image based
on the image data including the above-generated color-system
signal, the image data supplied to the display means is under the
influence of the de-gamma characteristic shown as an example in the
column (A) in Table 2. The de-gamma characteristic is expressed by
the following formula.
Out=((In/255){circumflex over ( )}2.22).times.255
[0235] Here, symbol Out denotes the output signal and symbol In
denotes the input signal, similarly to those in the above gamma
correction processing. In this case, the input signal In
corresponds to the color image signal including the chroma signal
subjected to the color correction processing. It is assumed that
the de-gamma correcting coefficient de.gamma. is equal to 2.22.
Here, symbol {circumflex over ( )} denotes the power. The de-gamma
characteristic is the same as that in the conventional image signal
processing system. Thus the influence of the de-gamma
characteristic is as follows. 17 Out ( R ) = ( ( In ( R ) / 255 ) ^
2.22 ) .times. 255 = ( ( 178 / 255 ) ^ 2.22 ) .times. 255 115 Out (
G ) = ( ( In ( G ) / 255 ) ^ 2.22 ) .times. 255 = ( ( 62 / 255 ) ^
2.22 ) .times. 255 11 Out ( B ) = ( ( In ( B ) / 255 ) ^ 2.22 )
.times. 255 = ( ( 88 / 255 ) ^ 2.22 ) .times. 255 24
[0236] Hence, the processing result of the gamma correction
processing is as shown in the column (B) in Table 2,
[0237] R signal=115,
[0238] G signal=11, and
[0239] B signal=24.
[0240] As mentioned above, the chroma signal under the influence of
the de-gamma characteristic has the same result as that of the
signal through the above color correction processing.
[0241] Namely, in the image signal processing system according to
the embodiment, the color correction processing of the color-system
signal is executed at an earlier stage than the gamma correction
processing upon generating the image data. When the image is
reproduced and displayed based on the above-generated image data,
the color is accurately reproduced.
[0242] In other words, in the image signal processing system
according to the embodiment, the color status of the reproduced and
displayed image is easily expected upon generating the image data.
Advantageously, the color correction processing is easy in
consideration of the image upon the reproducing and display
operation by using simple linear processing.
[0243] In the image signal processing system according to the
embodiment, the gamma correction processing of the Y signal is
implemented before the coring processing in the Y signal processing
system as shown in FIG. 1.
[0244] A description is given of the flow for the Y signal
processing system in the image signal processing system according
to the embodiment in consideration of the foregoing.
[0245] First, the output signal (color image signal) from the CCD
10 is inputted to the Y.gamma. unit 11. The Y.gamma. unit 11
performs the gamma correction processing of the Y signal.
[0246] FIG. 9 is a diagram showing the processing result of the
gamma correction processing in the image signal processing system
according to the embodiment. Referring to FIG. 9, the axis of
ordinate denotes the amount of noise and the axis of abscissa
denotes the amount of incident light, namely, image brightness.
[0247] As shown in FIG. 9, through the execution of the gamma
correction processing, the amount of noise of the input signal (the
output signal from the CCD 10) to the Y.gamma. unit 11 is
substantially constant irrespective of the image brightness.
[0248] The above-generated signal is sequentially subjected to the
edge emphasis processing. In this case, the LPF unit 13 performs
the edge emphasis processing. The processing result of the edge
emphasis processing is shown in FIG. 10.
[0249] FIG. 10 is a diagram showing the processing result of the
edge emphasis processing in the image signal processing system
according to the embodiment. Referring to FIG. 10, the axis of
ordinate denotes the amount of noise and the axis of abscissa
denotes the amount of incident light, namely, image brightness
(brightness).
[0250] As shown in FIG. 10, the amount of noise included in the
entire image signal through the edge emphasis processing is
increased overall as compared with the image signal before the
processing.
[0251] Next, the coring processing is executed based on the signal
subjected to the edge emphasis processing.
[0252] FIG. 11 is a diagram showing a set value of the coring
threshold level in the image signal processing system according to
the embodiment. Referring to FIG. 11, the axis of ordinate denotes
the amount of noise and the axis of abscissa denotes the amount of
incident light, namely, image brightness.
[0253] In the image signal processing system according to the
embodiment, the coring threshold level is set as shown by a dotted
line in FIG. 11. In this case, the coring threshold level
.vertline.a.vertline. is set to be constant irrespective of the
image brightness. Therefore, since the amount of noise included in
the target signal is substantially constant according to the
embodiment, the coring threshold level .vertline.a.vertline. is set
so as to remove substantially all the noise components. Thus, the
noise component is not emphasized irrespective of the image
brightness and, consequently, the signal after the coring
processing becomes the signal excluding substantially all the noise
component, namely, the signal nearly with the zero amount of noise,
irrespective of the image brightness, as shown in FIG. 12.
[0254] FIG. 12 is a diagram showing the processing result of the
coring processing in the image signal processing system according
to the embodiment. Referring to FIG. 12, the axis of ordinate
denotes the amount of noise and the axis of abscissa denotes the
amount of incident light, namely, image brightness.
[0255] As mentioned above, the image signal processing system
comprises the Y signal processing system and the chroma signal
processing system, independently, according to the first
embodiment. Thus, the band of the LPF unit 22 for limiting the band
is set to be narrow in the chroma signal processing system. It is
capable of providing the image signal processing system for always
generating the chroma signal (C signal) in one processing system
with the preferable S/N ratio without the influence to the
luminance signal (Y signal) generated in another processing system
and the camera using the image signal processing system.
[0256] In the image signal processing system according to the
embodiment, the Y signal generated in the Y signal processing
system is substantially the same as the Y signal used for
generating the chroma signal in the chroma signal processing
system. No contradiction exists between the Y signal and the chroma
signal generated in the image signal processing system, and the
color is always reproduced with accuracy.
[0257] That is, in the image signal processing system according to
the embodiment, the gamma correction processing of the Y signal is
performed before the execution of the Y signal generation
processing. By setting the gamma characteristics substantially
similarly in both the Y.gamma. unit 11 and the RGB.gamma. unit 23,
the addition processing is performed without contradiction in the
components between the generated wide-band Y signal and chroma
signal (CrCb).
[0258] Further, in the image signal processing system according to
the embodiment, the color correction processing is executed at an
earlier stage than the gamma correction processing in the
RGB.gamma. unit. Thus, the color correction processing is executed
in consideration of the image which is finally displayed.
[0259] Further, in the image signal processing system according to
the embodiment, the gamma correction processing is executed at an
earlier stage than the coring processing in the Y signal processing
system. Consequently, a substantially constant amount of coring
threshold level is set irrespective of the image brightness.
Substantially all the noise components are removed and the shortage
of the image resolution is easily solved in the low-luminance
area.
[0260] The output signal from the image pick-up device (CCD 10) is
explained as the color image signals (RGB) in the original color
system according to the embodiment. However, the present invention
is not limited to this and it is easily applied to the case of
using the image pick-up device for outputting the color image
signal of a complementary color system.
[0261] As mentioned above, the present invention provides the image
signal processing system capable of generating the preferable image
data by devising various signal processing executed based on the
image signal obtained by the image pick-up device and the camera
using the image signal processing system.
[0262] Another embodiment in which the above embodiment is partly
combined belongs to the present invention.
[0263] In this invention, it is apparent that working modes
different in a wide range can be formed on this basis of this
invention without departing from the sprit and scope of the
invention. This invention is not restricted by any specific
embodiment except being limited by the appended claims.
* * * * *